A major focus of the polyolefin industry in recent years has been on the development of new catalysts that deliver new and improved products. Transition metal catalysts, such as, for example, metallocene catalysts, are now widely used to produce polyolefin polymers, such as polyethylene polymers. Transition metal catalysts generally require an activator or cocatalyst in order to achieve commercially acceptable activity levels. Exemplary activators include methylalumoxane (MAO) and molecular activators or co-catalysts such as Lewis acidic boranes.
Further, for use in particle forming polymerization processes, such as gas phase processes, transition metal catalysts are typically supported on a particulate carrier. Often, the supported transition metal catalyst is utilized in the form of a free flowing powder requiring that the supported catalyst is vacuum dried during manufacture so as to remove the liquid diluent in which the catalyst is prepared. At commercial scale, where supported catalyst batch size may be of the order of 200 kg of solids or more, the vacuum drying step can be extremely time consuming, particularly where relatively high boiling point liquids, such as toluene, have to be removed. WO 99/26989 describes the preparation of a supported metallocene catalyst of about 550 kg batch size where the catalyst is prepared in toluene and then vacuum dried for at least 15 hours. WO 99/61486 describes the preparation of a supported metallocene catalyst also of about 550 kg batch size where the catalyst is vacuum dried for 15 hours. Such long drying times have a clear negative impact on the economics of catalyst production.
Therefore, it would be desirable to provide lower cost processes for preparing supported transition metal catalysts at large scale which also deliver catalysts capable of operating in a polymerization process with good productivity.